This invention relates to the field of medicine, for example, dentistry, and the mounting of all types of prostheses to osseointegrated implants.
Tooth loss in humans is an unfortunate fact of life for a large portion of the population. The concomitant loss of masticatory function and esthetics is a very real problem that has only been able to be effectively addressed by various treatment modalities in modern times. Traditional restorative treatment for tooth loss has been placement of fixed partial prostheses (bridgework), removable partial prostheses (partial dentures), and complete removable prostheses (complete dentures). The main shortcoming of all of these treatment modalities is the lack of underlying bone support for the prosthetic replacement, making the stability of some prostheses tenuous at best.
Osseointegrated dental implants have vastly improved this situation by providing solid bone support for all of the types of prostheses already mentioned. Currently, most dental implants have one of two basic designs. Both designs have an implant component that is surgically placed in either the maxilla or the mandiblle.
This surgical placement leaves a portion of the implant above the bone so that an abutment may be affixed to it. The abutment protrudes from the patients gum tissue, and it is on the abutment that the prosthesis is affixed. The manner of fixation of the abutment to the implant is what separates the two main designs. In one design, the abutment has threads machined into it, and it directly screws into the implant, while the other, more popular design, has a separate retaining screw to fix the abutment to the implant. Respectively, abutments are referred to as direct threading abutments and screw retained abutments. In either case, however, both types of abutments need to be tightened to a predetermined torque which accomplishes two things: 1) Application of proper torque limits the possibility of the shearing (failure) of the retaining screw or direct threading abutment due to the over application of torque. Retrieving sheared screw threads which remain inside the implant without damaging the implant itself is a virtual impossibility due to the miniature nature of the screw threads. 2) Proper application of torque limits the possibility of abutment loosening, which requires an office visit by the patient to resolve. These office visits to simply tighten a loose abutment are time consuming, costly and annoying not only for the patient, but the dentist as well.
Traditionally, direct threading abutments and screw retained abutments have been torqued with miniature ratchet torque limiting wrenches, which are costly to manufacture, assemble and calibrate. Unfortunately, after repeated use and more importantly, after repeated autoclaving, they lose their initial accuracy. As a result, these wrenches need to be returned to the manufacturer on a periodic basis to be recalibrated and/or repaired. Additionally, to maintain even some accuracy between recalibration procedures, these wrenches need to be disassembled and lubricated before each autoclaving cycle (between each patient use). So on top of being very expensive devices to purchase initially, the level of maintenance required to maintain acceptable accuracy in conventional ratchet style torque wrenches is an additional costly and unacceptable burden placed on the dentist. The net result is that only a limited number dentists who place large numbers of implants actually own an implant torque wrench, even though the benefits of properly torquing implant abutments are abundantly clear.
To make matters worse, because the dental implant market is still rather fragmented, each manufacturer has its own retaining screw head drive design and their own recommendations for application of torque. The net result is that there is no standardization of components or torque recommendations, and the torque wrench from one manufacturer will often be useless with another manufacturer's implant system because their torque wrenches by design have no adjustability or adaptability with other implant systems. Thus, if the dentist switches implant systems, he/she usually has to purchase a brand new expensive torque wrench to be used with the new system.
Also, in orthopedic implants, generally, there are applications in which an implant is screwed directly into the skeletal bone or into an abutment placed in the bone, e.g., spinal plates and cages. These implant techniques employ torque wrenches of various designs to limit the amount of torque placed on the implant.
U.S. Pat. No. 5,030,096 to Hurson et al illustrates a conventional dental implant that requires an insertable wrench to place the device.
Hollander, U.S. Pat. No. 6,162,053, describes a straight dental wrench with a spring loaded bearing. At a particular torque load the spring compression is overcome and the wrench is disabled.
Patterson et al, U.S. Pat. No. 5,295,831, teaches a dental wrench which has a weakened portion along a shaft that may be straight or bent. The shaft will deform at the weakened portion upon reaching the designed torque.
U.S. Pat. No. 5,347,894 to Fischer discloses a wrench for inserting halo pins in the skull. The wrench has two shear points which will break at a particular amount of torque. The device is designed so that the components of the wrench remain attached after shearing apart to prevent loss of parts.
Therefore, a need exists for a new torque limiting wrench that is simple in design, that is inexpensive to manufacture and purchase, that has the flexibility to economically adapt to any implant system on the market today or in the future, that requires absolutely no maintenance whatsoever, and that delivers torque with the safety and accuracy befitting the precision torque requirements of implants.